Polymer latex compound

ABSTRACT

A polymer latex composition has an acrylonitrile component, a polychloroprene component, and a natural latex component. When these components are blended together and formed into a film, the film exhibits a resistance to ozone that is greater than a resistance to ozone of materials in which acrylonitrile is not included. Furthermore, the combination of acrylonitrile and chloroprene imparts a synergistic effect to the composition with regard to ozone resistance. The film can be formed into a glove having a resistance to ozone that is improved over the resistance to ozone of gloves not including acrylonitrile. The glove may include an antimicrobial agent.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 12/189,352, filed on Aug. 11, 2008, and which claims thebenefit of U.S. Provisional Patent Application No. 60/964,096, filed onAug. 9, 2007, the contents of which are incorporated herein by referencein their entirety.

TECHNICAL FIELD

This disclosure relates to polymer formulations for compounds havingimproved resistance to ozone and, more particularly, to ozone-resistantcompounds incorporating multiple polymers that can be formed into rubberfilms for use in, for example, gloves, baby products, and the like.

BACKGROUND OF THE INVENTION

Latex is an aqueous suspension of hydrocarbon polymer. When thesuspended hydrocarbon polymer is coagulated using an acid or (as is morecommonly used) calcium nitrate, the coagulated material drops out of theaqueous phase as a solid. This solid can be of a single latex type, orit can be a combination of latex-type polymers. The hydrocarbonpolymer(s) suspended in the aqueous phase can be selected to provide aspecific formulated blend. When the latex is natural (derived from plantsources), a natural rubber product is produced. When the latex issynthetic (artificially produced using emulsion polymerizationtechniques), a synthetic rubber product is produced. For example, whenchloroprene monomers (2-chloro-1,3-butadiene) are polymerized (reactedto link into a chain), the resulting product is known as polychloropreneor chloroprene rubber, more commonly known by the trade name Neoprene,which is available from DuPont Performance Elastomers L.L.C. ofWilmington, Del., USA.

Naturally-occurring ozone gas is corrosive to natural rubber and causesit to degrade, thereby compromising the integrity of devices in whichnatural rubber is a component. Some synthetic rubbers, on the otherhand, exhibit a resistance to ozone that is superior in comparison tonatural rubber. Unfortunately, many synthetic rubbers and most notablythe highly ozone resistant chloroprene-based rubbers are currentlysignificantly higher in cost than natural rubber. To increase ozoneresistance to a rubber product, polychloroprene latex is blended withnatural latex in the compound formulation stage at a blend ratio levelto impart the ozone resistance of the polychloroprene to the overallmaterial. The higher the polychloroprene ratio to natural latex, thehigher ozone resistance will be.

To facilitate effective ozone resistance at a cost that is morereasonable given the cost of chloroprene rubber, rubber that is amixture of chloroprene rubber and natural rubber has been derived. Toproduce a very minimal ozone-resistant compound, the chloroprene contentis typically about 30% by weight (wt. %). This 30% chloroprene contentis only marginally better than natural rubber alone. About 40%polychloroprene is needed to cause a substantial increase in ozoneresistance to be realized. At 40%, there is a sufficient saturation ofpolychloroprene to cover the natural rubber particles and to providesuitable resistance to ozone degradation. The combination of naturalrubber and chloroprene rubber at the proper ratio thus allows thebenefits of both materials to be realized. More specifically, byblending the natural and chloroprene rubbers, ozone resistance from thepolychloroprene is realized, and elasticity, strength, and tearresistance from the natural rubber is realized. However, the high costof polychloroprene makes it a less than optimum material for use inrubber products, particularly at the levels currently used.

What is needed is a more cost-effective material that can be used inconjunction with polychloroprene to provide suitable ozone resistance torubber.

SUMMARY OF THE INVENTION

This patent describes substitution of a portion of the costlypolychloroprene with more cost-effective acrylonitrile latex to achieveequal or better ozone resistance than a low-ratio of polychloroprene tonatural latex blend, thereby increasing the ozone resistance at a morefavorable cost.

In one aspect, the present invention relates to a polymer latexcomposition having an acrylonitrile (2-propenenitrile) component, apolychloroprene component, and a natural latex component. When thesecomponents are blended together and formed into a film, the filmexhibits a resistance to ozone that is improved over the resistance toozone of materials in which acrylonitrile is not included. Furthermore,the combination of acrylonitrile and chloroprene imparts a synergisticeffect to the composition with regard to ozone resistance. Inparticular, the ozone resistance realized by the combination of theacrylonitrile and chloroprene with the natural latex is greater thaneither of the acrylonitrile and polychloroprene individually in naturalrubber.

In another aspect, the present invention relates to a glove fabricatedfrom a film of polymer latex composition as described herein (e.g.,about 20 wt. % acrylonitrile, about 20 wt. % polychloroprene, and about60 wt. % natural latex). The glove has a resistance to ozone that isimproved over the resistance to ozone of gloves not includingacrylonitrile.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a graphical comparison of the tensile strength for aselected modulus of various samples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the terms “acrylonitrile” and “nitrile” refer tobutadiene acrylonitrile copolymer or nitrile butadiene rubber (NBR). TheNBR used with regard to the present invention comprises carboxylatednitrile butadiene rubber.

As referred to herein, NBR is a family of unsaturated copolymers of2-propenenitrile and various butadiene monomers (e.g., 1,2-butadiene and1,3-butadiene) in which the acrylonitrile component is between about 20%and 50% and in which the butadiene component complements theacrylonitrile and is between about 80% and 50%. Although the physicaland chemical properties of NBR vary depending on the polymer compositionof the nitrile, it can be generally stated that more nitrile within thepolymer will produce a material of lower flexibility (as compared toless nitrile in the polymer producing a material of greaterflexibility). The carboxylation of the NBR provides carboxyl side groupsthat improve abrasion and wear resistance, ozone resistance, and lowtemperature flexibility as compared to non-carboxylated NBR.

The present invention utilizes a blend of acrylonitrile,polychloroprene, and natural latex to provide a rubber film havingdurability against the effects of ozone while allowing the rubber filmto maintain a suitable elasticity and a lower modulus of elasticity.Durability against the effects of ozone while maintaining elasticity andmodulus is not realized by the foregoing components individually or thecombination of any two of the components. Additionally, the cost ofacrylonitrile is much less than polychloroprene and approximately equalto the cost of natural latex.

The formulations of the present invention include acrylonitrile,polychloroprene, and natural latex in ratios of about 20/20/60, whichare formulations having 20% acrylonitrile, 20% polychloroprene, and 60%natural latex. The percentages of each component of the formulation maybe approximate. The formulations of the present invention, when blended,define polymers that are aqueous latex compounds. A latex compound ofsuch a polymer is cross-linked using a sulfur vulcanization process toproduce a rubber film. Using suitable manufacturing technology, thepolymer is capable of being processed into gloves, baby products such aspacifiers, baglets, bottle nipples, and the like, and a myriad of otherdevices. Depending upon the particular device into which the aqueouslatex compound is processed, the sulfur vulcanization process may beperformed before, during, or after the formation of device.

In one embodiment of the present invention, a polymer comprising about10 wt. % to about 30 wt. % acrylonitrile, about 10 wt. % to about 30 wt.% polychloroprene latex, and about 56 wt. % to about 64 wt. % naturallatex is processed to provide one polymer formulation (20/20/60) of thepresent invention. Preferably, the acrylonitrile is about 18 wt. % toabout 22 wt. % and the polychloroprene is about 18 wt. % to about 22 wt.%. The polymer formulation is based on the dry weight of each component.The acrylonitrile component may also include about 3 wt. % to about 7wt. % of a stabilizer (e.g., a soap) and is adjusted with a suitableamount of potassium hydroxide or the like to cause the component (whichis an aqueous solution) to be alkaline, preferably to a pH of about 10to about 11. The natural latex component includes about 2% to about 15%of at least one curing agent, accelerator, and an antioxidant in theform of an aqueous dispersion. The curing agent dispersion may be atypical rubber cure system combination (e.g., zinc oxide, sulfur, a cureaccelerator, and an antioxidant). The present invention is not limitedin this regard, however, as other similar cure systems are within thescope of the present invention. Also, the final compound may includeabout 2% to about 5% of a coloring agent and additionally (andoptionally) up to about 3% wax emulsion. This polymer formulation is notlimited in this regard, as other materials and amounts are within thescope of the present invention.

The acrylonitrile component in conjunction with the polychloroprenefacilitates the blending of the acrylonitrile with the natural latex. Inparticular, the combination of the acrylonitrile and the polychloropreneenhances the blending of the acrylonitrile/polychloroprene/natural latexcompound due to the stability of the polychloroprene, thereby improvingthe stability of blending process as well as the pot life of thecompound. On the other hand, various materials may also be added toallow the acrylonitrile, polychloroprene, and natural latex to blendtogether into a stable latex compound. For example, sodium alkylsulfate, which is an anionic stabilizer for natural, synthetic, andpolychloroprene latexes may be added. Also, a monosodium salt ofsulfated methyl oleate may be added to, for example, improve thesmoothness and gloss of the polychloroprene latex film and/or as amodifier for latex dipping compounds.

In another embodiment of the present invention, a glove comprises apolymer having about 10 wt. % to about 30 wt. % acrylonitrile, about 10wt. % to about 30 wt. % polychloroprene latex, and about 56 wt. % toabout 64 wt. % natural latex. Preferably, the acrylonitrile is about 18wt. % to about 22 wt. % and the polychloroprene is about 18 wt. % toabout 22 wt. %. Again, the polymer formulation is based on the dryweight of each component. The acrylonitrile can include about 3 wt. % toabout 7 wt. % stabilizer (e.g., a soap) and can be adjusted with asuitable base to bring the acrylonitrile into the alkaline range,preferably to a pH of about 10 to about 11. The natural latex componentincludes about 2% to about 15% of at least one curing agent,accelerator, and an antioxidant in the form of an aqueous dispersion.Colorants may be used to impart color to the finished glove product(typically about 2% to about 5%). Additionally, up to about 3% waxemulsion can also be added. The glove can be formed using any suitabletechnique (e.g., blow molding, casting, or the like).

An antimicrobial agent may be incorporated into the glove. Oneparticular antimicrobial agent that can be used is Ultra Fresh 15, whichis a 15% active, water-based dispersion of diiodomethyl-p-tolylsulfoneavailable from Thomson Research Associates of Toronto, Canada. The UltraFresh 15 (or any other antimicrobial agent) is added as a dispersion tothe glove material from which the glove is made. The present inventionis not limited to the use of Ultra Fresh 15, however, as otherantimicrobial agents are within the scope of the present invention.

The dispersion is incorporated into the polymer material used tomanufacture the glove by mixing of the dispersion into the liquid latexor latex/polychloroprene mixture. The latex or latex/polychloroprenemixture is itself an aqueous dispersion so the antimicrobial agent isreadily accepted and dispersed evenly throughout the compound.

In addition, the combination of the antimicrobial agent with otheractive materials can be suspended in a similar way and added to thelatex or latex/polychloroprene matrix. Other suitable materials thatcould be added include, for example, triclosan, fluorescent material,silver salt, biguanide, chlorohexidene salt, dextran sulfate, quaternaryammonium salt, benzalkonium, acriflavine, acridine dye, gentian violet,mercurochrome, extract of blue green algae, or any mixtures thereof. Thepresent invention is not so limited, however, as other materials may beadded.

Example 1 Formulation of Tripolymer Concept Used for Initial Testing

The formulation indicated below was used for initial testing of thepolymer incorporating acrylonitrile, polychloroprene, and natural latex.The resulting compound was used as the 20/20/60 composition insubsequent Examples.

% Wet % water Dry wt. Wet wt. Material ppH Active weight cut (lbs.)(lbs.) Nitrile 20.00 43.9 45.558 0.53 1.2 Sodium alkyl 0.25 33.0 0.75833 0.01 0.02 sulfate (water) 0.04 Monosodium 0.25 33.0 0.758 33 0.010.02 sulfated methyl oleate salt (water) 0.04 Wax emulsion 1.000 54.01.852 0.03 0.05 KOH 0.500 10.0 5.000 0.01 0.13 Chloroprene 20.00 50.040.00 0.53 1.05 Natural latex 60.00 60.0 100.0 1.58 2.63 ZnO dispersion3.00 50.0 6.000 0.08 0.16 Vulcanization 4.30 54.0 7.963 0.11 0.21 andAntioxidant dispersions Colorant 0.20 50.0 0.400 0.01 0.01 Sub-total109.5 208.5 2.88 5.57 Ultrafresh 15 0.5 grams Water 0.84 adjustmentTOTAL 109.5 208.5 2.88 6.41 The nitrile used was Reichhold 68073Nitrile, available from Dow Reichhold Specialty Latex LLC of ResearchTriangle Park, North Carolina, USA.

Example 2 Tensile Results of Films Based on Polymer Formulations

Various formulations of acrylonitrile/chloroprene/natural latex weretested to determine the tensile strength of films thereof.

TABLE 1 Summary of tensile testing results Sample Composition* Gauge100% 200% 300% 400% 500% 600% 700% Tensile Elongation (%) 1  0/30/700.0141 147 191 241 314 499 902 1574 3199 864 2 20/20/60 0.0132 198 287430 752 1353 2179 2832 2876 678 3 40/20/40 0.0133 285 437 685 1266 17742523 511 *wt. % acrylonitrile/wt. % chloroprene/wt. % natural latex

In the above Table 1, Sample 1 served as a control (no acrylonitrile).Gauge indicates the thickness of films.

Referring to the FIGURE, a comparison of the tensile strength for the300% modulus of each sample is made. The 300% modulus of Sample 1, asshown at 10, was substantially less than the 300% modulus of Sample 2,as shown at 20. Both were less than the 300% modulus of Sample 3, shownat 30. A tensile strength value 50 of Sample 2, however, issubstantially in line with a tensile strength value 40 of Sample 1 butsubstantially greater than a tensile strength value 60 of Sample 3. Thisindicates that an optimum amount of acrylonitrile occurs between 20 wt.% and 40 wt. %.

Example 3 Effects of Ozone on Films Based on Polymer Formulations

Sample discs of material were folded twice to generate a stress point.The sample discs were then placed into an ozone chamber operating at25-35 pphm ozone concentration. The samples were checked after everyhour and assigned a value (0-4 in 0.5 increments) based on the degree ofwear of the sample. An assigned value of 0 indicated that the sampleexperienced some whitening, but no cracks and no damage was visible; avalue of 1 indicated that small microscopic cracks were visible undermagnification, but the material was still usable; a value of 2 indicatedthat cracks were visible to the naked eye and about one half of the filmdepth; a value of 3 indicated that deep cracks were visible, but thematerial was still usable although weakened; and a value of 4 indicatedthat the film was split or splitting was imminent upon elongation. After21 hours, a summation of all values was taken.

TABLE 2 Samples Sample Composition* Sum 1  0/30/70 68 2 20/20/60 23.5 340/20/40 30.5 4  0/0/100 34 *wt. % acrylonitrile/wt. %polychloroprene/wt. % natural latex

From the above data, it can be seen that Sample 2 outperformed Sample 1and Sample 4.

Example 4 Effects of Ozone on Stretched Films Based on PolymerFormulations

Rubber films (plates) were prepared from a variety of formulationsdiffering in acrylonitrile, chloroprene, and natural rubber latexratios. Samples one inch wide were cut from the plates, elongated 50%,and stapled to cardboard mounts. The samples were placed in an ozonechamber and observed at 5, 10, 13, and 19 hours.

TABLE 3 Samples Sample Composition 1 20/20/60 2  0/30/70 4  0/0/100 5 40/0/60 *wt. % acrylonitrile/wt. % chloroprene/wt. % natural latex

The Samples were monitored and assessed for cracking, pitting, and othersurface damage. Samples 2 and 4 were completely destroyed by 13 hours,whereas Samples 1 and 5 showed no damage at the end of the same 13 hourperiod. At 19 hours, Sample 1 showed some whitening but no damage, andSample 5 showed minor surface fissures, some curling, and whitening. Itwas concluded that Sample 1 definitively outperformed Samples 2 and 4.

Similar testing at longer periods of time indicated that Sample 1 maycompete with samples having even higher chloroprene levels (e.g., 60%chloroprene and 40% natural latex).

Although this invention has been shown and described with respect to thedetailed embodiments thereof, it will be understood by those of skill inthe art that various changes may be made and equivalents may besubstituted for elements thereof without departing from the scope of theinvention. In addition, modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodimentsdisclosed in the above detailed description, but that the invention willinclude all embodiments falling within the scope of the appended claims.

1. A glove fabricated from a polymer latex compound and comprising: anacrylonitrile component; a polychloroprene component; and a naturallatex component; wherein said components are blended together andformable into a film having a resistance to ozone that is greater than aresistance to ozone of a compound without said acrylonitrile component;and wherein said film is formed into the shape of the glove.
 2. Theglove of claim 1, wherein said film is formed into the shape of theglove by a casting process.
 3. The glove of claim 1, wherein saidacrylonitrile component comprises about 10 wt. % to about 30 wt. %acrylonitrile.
 4. The glove of claim 1, wherein said acrylonitrilecomponent comprises about 18 wt. % to about 22 wt. % acrylonitrile. 5.The glove of claim 1, wherein said polychloroprene component comprisesabout 10 wt. % to about 30 wt. % polychloroprene.
 6. The glove of claim1, wherein said polychloroprene component comprises about 18 wt. % toabout 22 wt. % polychloroprene.
 7. The glove of claim 1, wherein saidnatural latex component comprises about 56 wt. % to about 64 wt. %natural latex.
 8. The glove of claim 1, further comprising about 3 wt. %to about 7 wt. % of a stabilizing agent.
 9. The glove of claim 1,further comprising an antimicrobial agent.
 10. The glove of claim 9,wherein said antimicrobial agent is diiodomethyl-p-tolylsulfone.
 11. Theclaim of claim 9, wherein said antimicrobial agent is selected from thegroup consisting of triclosan, fluorescent material, silver salt,biguanide, chlorohexidene salt, dextran sulfate, quaternary ammoniumsalt, benzalkonium, acriflavine, acridine dye, gentian violet,mercurochrome, extract of blue green algae, and mixtures thereof.